<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        div {
            color: #0000EE;
            cursor: pointer;
        }
    </style>
    <script>
        function changePic1() {
            document.querySelector('body iframe').src = "http://ichef.bbci.co.uk/naturelibrary/images/ic/credit/640x395/w/wo/woodpecker/woodpecker_1.jpg";
        }

        function changePic2() {
            document.querySelector('body iframe').src = "http://www.nashvillezoo.org/piciformes/images/piliated_wp.jpg";
        }
    </script>
</head>
<body>
    <iframe width="650" height="500">
    </iframe>
    <div onclick="changePic1()">Pic 1</div>
    <div onclick="changePic2()">Pic 2</div>
</body>
</html>